In recent years, the popularity of individually portioned containers for food products and particularly, dairy products, has rapidly increased and the need to package these products in a suitable manner such that they be served to customer, has been realized by the industry. However, to make these products economically viable, production rates must be fairly high. To achieve these production rates the prior art packaging machines have been designed such that the precise location of the container and a lid is not necessary and tolerance variations in both the lid and container do not appreciably affect the seal. One of the most popular methods of avoiding problems caused by tolerance variations is to provide an oversized lid such that the precise location of the lid relative to the flange is not necessary and the lid only need be generally located above a flanged container for a proper heat seal to result. However, damage to the portion of the lid overhanging the flange of the container can result, seriously detracting from the appearance of the product.
Machines, which generally fall into this category, are disclosed in U.S. Pat. Nos. 3,527,020, Mancini; 3,714,755, Phalin et al; 3,783,581, Pierce; 4,077,190, Agent et al and 4,176,507, Mancini.
My earlier U.S. Pat. No. 4,176,507 discloses an improved structure for controlling a lid of a series of interconnected lids during the heat sealing and provides increased control as the lid is still connected to the series of interconnected lids, until the heat seal operation has been commenced. During the heat sealing operation, the lid is cut from the series of interconnected lids thereby freeing the lids to realign within the conveyor in preparation for sealing the following container. In this way accumulative errors in the location of the series of interconnected lids are avoided as realignment occurs after each heat sealing operation. Thus improved alignment of the lids in the conveyor is achieved, however, the exact position of the container in the conveyor varies. To assure a good heat seal is provided oversized lids still are used.
One such method which uses an oversized lid and provides one possible solution to the overhang problem, is shown in U.S. Pat. No. 3,838,550 which issued to Mueller, Oct. 1, 1974. An oversized heat sealable lid is applied to each container and the resulting overhanging lid is pressed down along the sides of the container. With this method the precise location of a precut lid relative to a container is not required, however, the resulting product even with the overhanging lid portion pressed downward has the appearance of poor workmanship. This problem is further compounded by damage during shipment where the overhanging portion of the lid becomes tattered.
Although these methods ensure a good heat seal between the lid and the container, the resulting product has the appearance of being produced by a cheap process and if the overhanging portion of the lid becomes crimped or torn it leads to the appearance of shoddy workmanship and the suggestion that the product has been tampered with. Therefore, it is desirable to produce a product where the precut lid is of sufficient area to cover the container and align the lid for heat sealing, such that the lid does not overhang the flange after it has been sealed in place. The only exception to this being the tab portion of the lid which projects outwardly from the flange, such that the lid may be removed.
In some applications, a continuous sheet has been applied over nested containers and a dye cutting operation is used to cut out the sealed lid from the sheet material and in some circumstances this cutting operation also dye cuts the container flange. Although this system provides a lid which is precisely located above a container flange the economy and convenience of precut and preprinted lids is not realized.
The present invention overcomes the disadvantages of the prior art machines and process.